The present invention relates to a gas purification-treating agent and a gas purifying apparatus, more specifically to a gas purification-treating agent and a gas purifying apparatus which remove carbon monoxide and/or hydrogen contained in a gas by effecting oxidation reaction in the presence of oxygen, and which also remove carbon dioxide and/or water formed by the oxidation reaction together with carbon dioxide and/or water contained originally in the gas, and particularly to a gas purification-treating agent and a gas purifying apparatus, in a system where air is sucked and compressed and the compressed gas is fed as a raw gas to an air separation plant, which effect oxidization of carbon monoxide and/or hydrogen to remove such impurities from the compressed air.
Conventionally, when carbon monoxide and/or hydrogen contained in a gas are/is to be removed, it is carried out generally to remove first the substantial part of water contained originally in the gas, i.e. the water formed by condensation under compression, and then to convert carbon monoxide and/or hydrogen by catalytic reaction into carbon dioxide and/or water which are/is then removed by adsorption together with the residual water of condensation and carbon dioxide contained originally in the gas.
For example, in an air separation plant for producing oxygen, nitrogen, etc., the impurities such as water and carbon dioxide contained in the raw air are removed by adsorption to an adsorbent such as activated alumina and zeolite. However, carbon monoxide and hydrogen which are contained each in an amount of about 1 to 5 ppm in the atmospheric air cannot be removed by using the adsorbent for adsorbing and removing carbon dioxide and water. Meanwhile, it is difficult to remove carbon monoxide by means of distillation, because the boiling point of carbon monoxide is close to that of nitrogen, so that carbon monoxide remains as an impurity in the product nitrogen, resulting in the failure of producing a high-purity nitrogen gas, disadvantageously. Meanwhile, hydrogen, which has a low boiling point, can be separated by means of distillation. However, a distillation plate must be additionally installed so as to achieve separation of nitrogen and hydrogen.
Accordingly, as shown in FIG. 12, raw air supplied to an air inlet 1 is introduced through a filter 2 and a passage 3 to an air compressor 4 to be compressed there, and the compressed raw air is fed through an after-cooler 5 and a water separator 6 and further through a passage 7 to a preheater 8 which is a heat exchanger and then introduced through a passage 9 to a heater 10 to be heated there. The thus treated raw air is introduced through a passage 11 to a catalyst column 12 where it is brought into contact with a carbon monoxide oxidizing catalyst and a hydrogen oxidizing catalyst to effect reaction with the oxygen contained in the air and to convert carbon monoxide and hydrogen into carbon dioxide and water respectively. The compressed air which contained carbon dioxide and water is then introduced through a passage 13 to the preheater 8 where their temperatures are lowered, and after they are introduced through passages 14 and 15 to a cooler 16 and cooled therein, they are further introduced through a passage 17 and through either a passage 18a or 18b to either an adsorption unit 19a or an adsorption unit 19b where carbon dioxide and water contained originally in the raw air supplied are adsorbed and removed, by an adsorbent packed in the adsorption unit 19a or that in the unit 19b, together with the carbon dioxide and water formed by catalytic oxidation. The raw air thus purified is designed to be supplied through either a passage 20a or a passage 20b and through a passage 21 to an air separation plant 22.
In the case where. a catalyst layer is incorporated in the system as shown in FIG. 12, the atmospheric air is brought into contact with the catalyst without going through any purifying means, so that the catalyst is deteriorated by catalyst poisons such as sulfur oxides contained in the atmospheric air. Accordingly, catalysts are used under heating as a measure for maintaining the catalytic activity. However, this requires electric power for heating a large amount of air, and even if the heat quantity required is reduced by heat recovery, a large heat exchanger is necessary for the recovery.
Meanwhile, in order to minimize the influence of catalyst poisons, it can be expected to install an adsorption unit for adsorbing and removing carbon dioxide and water contained originally in the air on the upstream side of the catalyst layer for catalyzing oxidation of carbon monoxide and/or hydrogen. According to this procedure, many catalyst poison can be removed by the purification action of the adsorbent, and the life of the catalyst can be improved. However, in this case, an extra adsorbent layer for adsorbing and removing carbon dioxide formed by oxidation of carbon monoxide and water formed by oxidation of hydrogen must be incorporated on the downstream side of the catalyst layer, requiring a high facility cost.
There are an affluence of literatures on oxidation catalysts for carbon monoxide and hydrogen describing a number of useful catalysts (e.g., Y. Murakami""s, xe2x80x9cSHOKUBAI REKKA MEKANIZUMU TO BOSHI TAISAKU (Catalyst Deterioration Mechanism and Its Prevention)xe2x80x9d, published by Gijutsu-Joho Kyokai, 1995). In these literatures, there are general descriptions of the deterioration of catalysts (reduction in the catalytic activities), but there is found no literature describing deterioration of catalysts in removing very small amount of carbon monoxide and hydrogen contained in the atmospheric air as is discussed in the present invention.
Under the present circumstances, catalysts are maintained at high temperatures of 100xc2x0 C. or higher in the conventional gas purifying apparatuses so as to maintain their activities based on the general consideration on catalytic reactions. However, in order to reduce electric power consumption rate in cryogenic separation of air, it is economically disadvantageous to heat a large amount of air as described above, and there has been expected an advent of catalysts having high activities of oxidizing carbon monoxide and/or hydrogen in the temperature range of about 5 to 50xc2x0 C. and an apparatus enabling extended use of catalysts without deterioration.
It is an objective of the invention to provide a gas purification-treating agent and a gas purifying apparatus which can remove carbon monoxide and/or hydrogen from a gas employing no special equipment.
Another objective of the invention is to provide a gas purifying apparatus realizing simplification of the conventional intricate pretreatment purification procedures including removal of carbon dioxide and water from a gas having passed through a carbon monoxide/hydrogen removing catalyst column, and downsizing of the apparatus.
The gas purification-treating agent and gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas according to the present invention are of the following constitutions and actions.
A first aspect of the present invention is a gas purification-treating agent for treating carbon monoxide and/or hydrogen contained in a gas in the presence of oxygen, and the agent consists of an adsorbent having carbon dioxide and/or water adsorptivity, and a metal or metal compound, carried thereon, which activates oxidation reaction of carbon monoxide and/or hydrogen. The adsorbent adsorbs carbon dioxide and/or water contained originally in the gas, as well as, carbon dioxide and/or water to be formed by the oxidation reaction of carbon monoxide and/or hydrogen. By subjecting the gas to purification treatment with this gas purification-treating agent, the carbon monoxide and/or hydrogen contained in the gas are/is oxidized in the presence of oxygen by the metal or metal compound which activates the oxidation reaction of carbon monoxide and/or hydrogen to convert them/it into carbon dioxide and/or water, respectively, and the carbon dioxide and/or water obtained by the oxidation treatment are/is adsorbed and removed by the adsorbent carrying the metal or metal compound thereon. Simultaneously, the carbon dioxide and/or water contained originally in the gas are/is also adsorbed and removed by the adsorbent.
A second aspect of the invention is that the gas purification-treating agent consists of an adsorbent having excellent water adsorptivity, and at least one of an Au-on-metal oxide, an Au-on-metal hydroxide and an Au colloidal powder carried thereon. When a gas containing carbon monoxide and/or hydrogen is to be purified using this gas purification-treating agent in the presence of oxygen, the reaction and treatment can be carried out at a relatively low temperature in the range of 0 to 100xc2x0 C., preferably 0 to 50xc2x0 C. Simultaneously, the carbon dioxide and/or water contained originally in the gas can also be adsorbed and removed. The adsorbent having excellent water adsorptivity includes, for example, activated alumina and silica gel.
A third aspect of the invention is that the gas purification-treating agent consists of an adsorbent having carbon dioxide adsorptivity and water adsorptivity, and at least one of an Au-on-metal oxide, an Au-on-metal hydroxide and an Au colloidal powder carried thereon. When a gas containing carbon monoxide and/or hydrogen is to be purified using this gas purification-treating agent in the presence of oxygen, the reaction and treatment can be carried out at a relatively low temperature in the range of 0 to 100xc2x0 C., preferably 0 to 50xc2x0 C. Simultaneously, the carbon dioxide and/or water contained originally in the gas can also be adsorbed and removed. The adsorbent having carbon dioxide adsorptivity and water adsorptivity includes, for example, various types of zeolites, and there is preferably selected Na-X type, Ca-A type or Ca-X type zeolite having preferably a CO2 equilibrium amount adsorbed of 0.3 mmol/g or more under a CO2 partial pressure of 0.25 kPa and at a temperature of 20xc2x0 C.
A fourth aspect of the invention is that the Au-on-metal oxide is at least one of Au/xcex1-Fe2O3, Au/TiO2, Au/SnO2, AuZnO2, Au/Co3O4, Au/NiO, Au/InO2 and Au/NiFeO4; whereas the Au-on-metal hydroxide is at least one of Au/Mg(OH)2 and Au/Be(OH)2. These oxides and hydroxides cause oxidation reaction of carbon monoxide and/or hydrogen to take place in the presence of oxygen at a relatively low temperature in the range of 0 to 100xc2x0 C.
A fifth aspect of the invention is that the gas purification-treating agent consists of an adsorbent which is a porous carrier having excellent water adsorptivity, and palladium and/or platinum carried thereon. When a gas containing carbon monoxide and/or hydrogen is to be purified using this gas purification-treating agent in the presence of oxygen, the reaction and treatment can be carried out at a relatively low temperature in the range of 0 to 50xc2x0 C. Simultaneously, the carbon dioxide and/or water contained originally in the gas can also be adsorbed and removed. The adsorbent having excellent water adsorptivity includes, for example, activated alumina and silica gel.
A sixth aspect of the invention is that the gas purification-treating agent consists of an adsorbent having carbon dioxide adsorptivity and water adsorptivity, and palladium and/or platinum carried thereon. When a gas containing carbon monoxide and/or hydrogen is to be purified using this gas purification-treating agent in the presence of oxygen, the reaction and treatment can be carried out at a relatively low temperature in the range of 0 to 50xc2x0 C. Simultaneously, the carbon dioxide and/or water contained originally in the gas can also be adsorbed and removed. The adsorbent having excellent carbon dioxide adsorptivity and water adsorptivity includes, for example, various types of zeolites, as given referring to the third aspect of the invention.
A seventh aspect of the invention is a gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas, provided with a container having a gas inlet and a gas outlet and packed with a treating agent consisting of an adsorbent for adsorbing carbon dioxide and water, and a metal or metal oxide, carried thereon, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen. Accordingly, the carbon monoxide and/or hydrogen contained in the gas introduced through the gas inlet into the container are/is oxidized with the aid of the metal catalyst in the presence of oxygen to be converted into carbon dioxide and/or water, which are/is then adsorbed and removed by the adsorbent carrying thereon the catalyst metal (a metal or metal compound which activates oxidation reaction of carbon monoxide and/or hydrogen; the same shall apply hereinafter). The thus treated gas is delivered as a purified gas from the gas outlet of the container. Incidentally, when the gas contains originally carbon dioxide and/or water, they are also adsorbed and removed by the adsorbent carrying thereon the catalyst metal.
An eighth aspect of the invention is a gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas, and the apparatus contains a first treating agent layer consisting of an adsorbent having excellent water adsorptivity, and a metal or metal compound, carried on the adsorbent, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen; and a second treating agent layer containing a treating agent consisting of an adsorbent having carbon dioxide adsorptivity and a metal or metal compound, carried thereon, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen; This adsorbent may of course have water adsorptivity additionally. The first and second treating agent layers being packed in a container having a gas inlet and a gas outlet in this order in terms of the gas flow. Accordingly, carbon monoxide and/or hydrogen contained in the gas introduced through the gas inlet into the container are/is oxidized in the presence of oxygen by the metal catalyst of the first treating agent layer to be converted into carbon monoxide and/or water. The water formed by the oxidation treatment, as well as, the water contained originally in the gas are first adsorbed and removed by the water adsorbent carrying the metal catalyst thereon, and then the carbon dioxide formed by the oxidation treatment, as well as, the carbon dioxide contained originally in the gas are adsorbed and removed by the carbon dioxide adsorbent carrying the metal oxide thereon in the second treating agent layer. The thus treated gas is delivered as a purified gas through the gas outlet of the container.
A ninth aspect of the invention is a gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas, and the apparatus contains a first adsorbent layer containing an adsorbent for removing water contained in the gas; a second adsorbent layer containing an adsorbent for removing carbon dioxide contained in the gas; and a treating agent layer containing a treating agent consisting of an adsorbent having carbon dioxide and/or water adsorptivity, and a metal or metal compound, carried on the adsorbent, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen; the first and second adsorbent layers and the treating agent layer being packed in a container having a gas inlet and a gas outlet in this order in terms of the gas flow. Accordingly, when a raw gas containing carbon monoxide and/or hydrogen is introduced into the first adsorbent layer, water if contained originally in the gas is adsorbed and removed in the first adsorbent layer and then introduced into the second adsorbent layer where carbon dioxide if contained originally in the raw gas is adsorbed and removed. The thus treated gas is introduced into the treating agent layer where carbon monoxide and/or hydrogen contained therein are/is oxidized in the presence of oxygen by the metal catalyst to be converted into carbon dioxide and/or water which are/is adsorbed and removed by the adsorbent carrying the catalyst metal thereon, and the thus treated gas is delivered as a purified gas. In this case, even if water and carbon dioxide failed to be adsorbed and removed in the first adsorbent layer and in the second adsorbent layer respectively, they are adsorbed and removed together with the carbon dioxide and/or water formed by the oxidation treatment in the treating agent layer containing the adsorbent carrying the catalyst metal thereon.
Incidentally, the adsorbent to be packed for forming the first adsorbent layer for adsorbing and removing water includes activated alumina, silica gel, etc.; whereas the adsorbent to be packed for forming the second adsorbent layer for removing carbon dioxide includes various types of zeolites and can be selected from those as used in the third aspect. Meanwhile, the treating agent consisting of an adsorbent carrying a catalyst metal thereon and constituting the treating agent layer is at least one of the treating agents as described in the first to sixth aspects.
A tenth aspect of the invention is a gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas, and the apparatus contains a first adsorbent layer containing an adsorbent for removing water contained in the gas, a second adsorbent layer containing an adsorbent for removing carbon dioxide contained in the gas; and a treating agent layer containing a mixture of a plurality of treating agents each consisting of an adsorbent having carbon dioxide and/or water adsorptivity, and a metal or metal compound, carried on the adsorbent, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen; the first and second adsorbent layers and the treating agent layer being packed in a container having a gas inlet and a gas outlet in this order in terms of the gas flow. Accordingly, when a raw gas containing carbon monoxide and/or hydrogen is introduced into the first adsorbent layer, water if contained originally in the gas is adsorbed and removed in the first adsorbent layer and then introduced into the second adsorbent layer where carbon dioxide if contained originally in the raw gas is adsorbed and removed. The thus treated gas is introduced into the treating agent layer where carbon monoxide and/or hydrogen contained therein are/is oxidized in the presence of oxygen by the metal catalyst to be converted into carbon dioxide and/or water which are/is adsorbed and removed by the adsorbent carrying the catalyst metal thereon. In this case, since the treating agent layer is of a mixture of a plurality of treating agents, it can securely provide a temperature range where the catalytic reactions take place stably.
Generally, in adsorption units for removing carbon dioxide and water contained in raw air, which are installed as pretreating units for air separation plants, in many cases, activated alumina, silica gel, etc. are packed on the raw air inlet side as adsorbents (driers) for adsorbing and removing water contained in the raw air; while zeolite is packed on the raw gas outlet side as an adsorbent for adsorbing and removing carbon dioxide. Accordingly, while the carbon monoxide and/or hydrogen treating agent layer may be located at any position on the downstream side (in terms of the gas flow) of the water adsorbent, the present inventors clarified in order to make the most of the performance of the carbon monoxide and/or hydrogen treating agent that a stable effect can be obtained in a specific temperature range if the treating agent layer is located on the downstream side of the carbon dioxide adsorbent, or if the water removing adsorbent layer, the carbon dioxide removing adsorbent layer, and the carbon monoxide and/or hydrogen treating agent layer are arranged in this order.
Further, in the eighth, ninth and tenth aspects described above, while it is desirable to pack each adsorbent layer and each treating agent layer separately layerwise in a single container having a gas inlet and a gas outlet in view of curtailment of facility cost, they may be packed into a plurality of containers each having a gas inlet and a gas outlet and arranged in series in the above-described orders respectively. Such constitutions are of course included in the present invention.
An eleventh aspect of the invention is a gas purifying apparatus for removing carbon monoxide and/or hydrogen contained in a gas, and the apparatus contains an adsorbent layer containing an adsorbent for adsorbing and removing water contained in the gas; and a treating agent layer containing a mixture of an adsorbent for adsorbing and removing carbon dioxide contained in the gas and a treating agent consisting of an adsorbent for adsorbing and removing carbon dioxide, and a metal or metal compound, carried on the adsorbent, for effecting oxidation treatment of carbon monoxide and/or hydrogen in the presence of oxygen; the adsorbent layer and the treating agent layer being packed in a container having a gas inlet and a gas outlet in this order in terms of the gas flow. This is the case where a mixture of the carbon dioxide adsorbent layer and the catalyst-containing treating agent layer in the ninth or tenth aspect is packed into the columns and is employed in view of the low cost compared with the case where the respective layers are packed into different containers, ease of packing procedures, etc.
Further, in the ninth and tenth aspects described above, a water and carbon dioxide adsorbent may be admixed to the treating agent layer. In the eleventh aspect, a water adsorbent may be admixed to the treating agent layer. Incidentally, the seventh to eleventh aspects are suitable for achieving purification of a gas containing carbon monoxide and/or hydrogen in a concentration on the order of ppm or less.
Meanwhile, the eighth to eleventh aspects are most suitable for achieving purification of raw air to be supplied to air separation plants.
Further, in the oxidation treatment of carbon monoxide and/or hydrogen, the oxygen contained originally in the raw gas and/or oxygen added separately are/is used.
A twelfth aspect of the invention is a gas purifying apparatus according to any of the seventh to eleventh aspects, wherein the carbon monoxide and/or hydrogen treating agent consists of an adsorbent of a porous carrier having excellent water adsorptivity, and palladium and/or platinum carried thereon. This treating agent can suitably be employed in the seventh to eleventh aspects of the present invention.
A thirteenth aspect of the invention is a gas purifying apparatus according to any of the seventh to eleventh aspects, wherein the carbon monoxide and/or hydrogen treating agent consists of an adsorbent having carbon dioxide adsorptivity and water adsorptivity, and palladium and/or platinum carried thereon. This treating agent can suitably be employed in the seventh to eleventh aspects of the present invention.
A fourteenth aspect of the invention is a gas purifying apparatus according to any of the seventh to eleventh aspects, wherein the carbon monoxide and/or hydrogen treating agent consists of an adsorbent having carbon dioxide and/or water adsorptivity, and Au/xcex1-Fe2O3 and/or an Au colloidal powder carried thereon. This treating agent can suitably be employed in the seventh to eleventh aspects of the present invention.
According to the present invention, carbon monoxide and/or hydrogen can be removed efficiently with no heating procedures and the like for enhancing the activity of carbon monoxide and/or hydrogen. The gas purification-treating agent and gas purifying apparatuses described above are most suitably employed in and as a pretreating purifying apparatus for an air separation plant for producing extremely high-purity nitrogen gas to be employed in semiconductor industries and the like. That is, carbon monoxide and/or hydrogen contained in air can be removed using substantially the same apparatus as the conventional pretreating apparatus for removing carbon dioxide and water and with substantially the same operation procedures.